The invention relates to a drive device having an electric drive motor, a casing, preferably with a casing cover, with at least one shaft driven by the drive motor and with compensating means to compensate for the axial lash of the shaft, where the compensating means contain at least one axially deformable elastomer element with at least one contact surface. The invention also relates to such an elastomer element.
In the following, description the shaft driven by the drive motor is understood to mean an output shaft driven by a drive motor through a gear, specifically a worm gear, as well as an armature shaft driven directly by the drive motor.
Drive devices of this kind find a use particularly in vehicles as actuator motors for seat adjustments, steering column adjustments, window regulators, sliding sunroofs, and as drive devices for windshield wiper systems. The drive devices normally have a worm gear connected in series with the drive motor, the gear being advantageously of small dimensions, capable of transmitting high levels of power and being self-locking.
Specifically because of the tapered flanks of the worm shafts and of the worm wheel in a worm gear of this type, an axial force acts on the armature shaft of the drive motor during operation of the drive device, as well as on the output shaft of the worm gear. The direction of the axial forces depends on the direction of rotation of the armature shaft. With a change in direction of the drive motor or a change in external load, the direction of the axial force on the armature shaft as well as on the output shaft is reversed, because the worm wheel is loaded in the opposite direction. Because of manufacturing tolerances in the individual components of the drive device and because of operating wear in the area of the axial bearings of the shaft, relatively large, undesirable axial lash can develop in the various shafts. As a consequence of axial lash of this kind, abrupt starting motions and irritating noises can result when the drive motor reverses direction. In addition, it is difficult to achieve precise positioning when starting or reversing a window that is being opened, for example, or a sliding sunroof.
Furthermore, noticeable relative motions can result if the drive device is used, for example, as an actuator motor for a seat back adjuster, and the driver perceives the axial lash as a relative motion of the seat back, even when the motor is not running. This phenomenon is additionally known in the case of steering column adjustments.
A drive device of this type is know from DE 38 15 356 A1 which has a contact button at the free end of the shaft as a compensating means to compensate for axial lash in a shaft, the button bearing against the contact surface of a carbide plate of a rubber-like carbide component, where the layer of rubber is disposed between the carbide plate and the drive device casing. A device of this kind has the disadvantage that firstly the contact button as well as the carbide plate have to be of hardened material in order to be able to withstand the extremely high pressure forces acting locally on the plate or the contact surface, respectively, without damage to the contact button or to the carbide plate. Furthermore, because of the weight of the carbide, a device of this kind has a relatively high overall weight, which cannot be ignored.
The object of the present invention is therefore to eliminate the previously enumerated disadvantages of the prior art.